Vanadium self-intercalated C/V1.11S2 nanosheets with abundant active sites for enhanced electro-catalytic hydrogen evolution

Enhancing Metallicity and Basal Plane Reactivity of 2D Materials via Self-Intercalation

Intercalation (ic) of metal atoms into the van der Waals (vdW) gap of layered materials constitutes a facile strategy to create materials whose properties can be tuned via the concentration of the intercalated atoms. Here we perform systematic density functional theory calculations to explore various properties of an emergent class of crystalline 2D materials (ic-2D materials) comprising vdW homobilayers with native metal atoms on a sublattice of intercalation sites. From an initial set of 1348 ic-2D materials, generated from 77 vdW homobilayers, we find 95 structures with good thermodynamic stability (formation energy within 200 meV/atom of the convex hull). A significant fraction of the semiconducting host materials are found to undergo an insulator to metal transition upon self-intercalation, with only PdS2, PdSe2, and GeS2 maintaining a finite electronic gap. In five cases, self-intercalation introduces magnetism. In general, self-intercalation is found to promote metallicity and enhance the chemical reactivity on the basal plane. Based on the calculated H binding energy, we find that self-intercalated SnS2 and Hf3Te2 are promising candidates for hydrogen evolution catalysis. All the stable ic-2D structures and their calculated properties can be explored in the open C2DB database.

Defect-Engineered VS2 Electrocatalysts for Lithium-Sulfur Batteries

Defective two-dimensional transition metal dichalcogenides can be effective electrocatalysts for Li-S batteries, but the relationship between defect types and battery performance is unclear. In this work, we designed S vacancy-type SV-VS2 and V self-intercalated-type VI-VS2 and measured their catalytic activities in Li-S batteries. Compared with self-intercalating V atoms, S vacancies accelerated Li+ diffusion and SV-VS2 as a Li+ "reservoir" promoted the sulfur conversion kinetics significantly. In addition, the presence of sulfur vacancies promoted the lithiation behavior of SV-VS2 during discharge, leading to an enhancement of the catalytic ability of SV-VS2. However, this lithiation phenomenon weakened the catalytic activity of VI-VS2. Overall, SV-VS2 had better adsorption and catalytic activity. Li-S batteries with SV-VS2-coated separators delivered high rate performance and excellent cycling stability, with a capacity decay rate of 0.043% over 880 cycles at 1.0 C. This work provides an effective strategy for designing efficient Li-S battery electrocatalysts using defect engineering.

Morphology-Controlled Synthesis of V1.11S2 for Electrocatalytic Hydrogen Evolution Reaction in Acid Media

High-performance low-cost catalysts are in high demand for the hydrogen evolution reaction (HER). In the present study, we reported that V_1.11S₂ materials with flower-like, flake-like, and porous morphologies were successfully synthesized by hydrothermal synthesis and subsequent calcination. The effects of morphology on hydrogen evolution performance were studied. Results show that flower-like V_1.11S₂ exhibits the best electrocatalytic activity for HER, achieving both high activity and preferable stability in 0.5 M H₂SO₄ solution. The main reason can be ascribed to the abundance of catalytically active sites and low charge transfer resistance.

Oxygen Vacancies and Interface Engineering on Amorphous/Crystalline CrOx -Ni3 N Heterostructures toward High-Durability and Kinetically Accelerated Water Splitting

Manipulating catalytic active sites and reaction kinetics in alkaline media is crucial for rationally designing mighty water-splitting electrocatalysts with high efficiency. Herein, the coupling between oxygen vacancies and interface engineering is highlighted to fabricate a novel amorphous/crystalline CrO_x -Ni₃ N heterostructure grown on Ni foam for accelerating the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory (DFT) calculations reveal that the electron transfer from amorphous CrO_x to Ni₃ N at the interfaces, and the optimized Gibbs free energies of H₂ O dissociation (ΔG_H-OH ) and H adsorption (ΔG_H ) in the amorphous/crystalline CrO_x -Ni₃ N heterostructure are conducive to the superior and stable HER activity. Experimental data confirm that numerous oxygen vacancies and amorphous/crystalline interfaces in the CrO_x -Ni₃ N catalysts are favorable for abundant accessible active sites and enhanced intrinsic activity, resulting in excellent catalytic performances for HER and OER. Additionally, the in situ reconstruction of CrO_x -Ni₃ N into highly active Ni₃ N/Ni(OH)₂ is responsible for the optimized OER performance in a long-term stability test. Eventually, an alkaline electrolyzer using CrO_x -Ni₃ N as both cathode and anode has a low cell voltage of 1.53 V at 10 mA cm^-2 , together with extraordinary durability for 500 h, revealing its potential in industrial applications.

Porous Co3O4 stabilized VS2 nanosheets obtained with a MOF template for the efficient HER

TS-Co₃O₄@VS₂ with highly efficient and stable catalytic hydrogen production performance was synthesized by the MOF template method hydrothermally.

2D heterogeneous vanadium compound interfacial modulation enhanced synergistic catalytic hydrogen evolution for full pH range seawater splitting

A novel electrocatalytic material VS2@V2C was proposed for the first time and successfully prepared by a one-step hydrothermal method. T-VS2 nanosheets were uniformly and vertically embedded on the V2C (MXene) matrix with a fewer layer structure. Owing to the fast charge transfer process at the interface of the two-phase structure and good conductivity, the composite material showed a lower hydrogen evolution overpotential and a very low Tafel slope in highly alkaline and highly acidic electrolytes (164 mV and 47.6 mV dec-1 in 1.0 M KOH; 138 mV and 37.9 mV dec-1 in 0.5 M H2SO4) under a current density of 20 mV cm-2. More importantly, high-efficiency and stable electrolysis of seawater was achieved at a current density greater than 100 mA cm-2, and the catalytic performance was significantly better than that of platinum-based alloys. First-principles calculations mechanically confirmed that VS2@V2C had higher carrier mobility and lower free energy of hydrogen adsorption. The VS2 nanosheets that grew outwards could provide support to avoid agglomeration on the catalyst surface and the edge sulfur sites of VS2 could promote the binding of adsorbed hydrogen atoms and the desorption of hydrogen molecules. Our work is expected to provide a valuable reference for the design and synthesis of the structure of industrial catalysts for hydrogen production from seawater in the future.

Metallic 1T-VS2 nanosheets featuring V2+ self-doping and mesopores towards an efficient hydrogen evolution reaction

Metallic 1T-VS₂ nanosheets featuring V²⁺-doping and plenty of mesopores have abundant defects and high conductivity and exhibit superior catalytic activity for electrochemical water splitting.